The present invention relates to valve operating apparatus for an internal combustion engine. More particularly, the invention involves valve operating apparatus of the type including a camshaft rotatably driven by the engine, a plurality of cams on the camshaft for operating the intake or exhaust valves according to a selected mode of operation, and pivotably mounted rocker arms or cam followers for opening and closing the valves in response to rotation of the cams.
In valve operating devices of the type described, driver cam followers, operably connected to the valve or valves to be operated, and free cam followers, independent of the valves, are disposed adjacent each other and are operable in different modes by rotation of the cams. A selective coupling carried by the cam followers is actuable for selectively interconnecting or disconnecting the respective cam followers according to the desired mode of valve operation. Resilient biasing means are employed for urging the free cam follower toward its associated cam.
In prior art valve operating devices of this type, the resilient biasing means comprises a single spring disposed between the free cam follower and the engine body for resiliently urging the free cam follower toward the camshaft. Such a device is disclosed in Japanese Laid-Open Patent Publication No. 61-19911.
When the cam followers in such apparatus are to be interconnected by the selective coupling, it is preferable for the spring to have a low set load in order to allow the free cam follower to swing slightly so that the cam followers can be interconnected while permitting some dimensional tolerances. However, when the valve operating device operates at a high speed, it is desirable that the spring for lifting the free cam follower have a greater spring load than that required to accommodate dimensional tolerances. If the lifting load is produced by a single spring, the spring constant of the spring would, of necessity, be quite large, making it difficult to reduce the set load of the spring to accommodate dimensional tolerances. Consequently, where components of the valve operation device have manufacturing tolerances, and the space for accommodating the spring has a greater length in the direction in which the spring exerts resilient forces than the free length of the spring, the free cam follower cannot properly be held in position by the spring, thereby resulting in functional problems associated with the selective connection and disconnection of the cam followers.
It is to the amelioration of this problem, therefore, that the present invention is directed.